Insights into the helium bubbles coarsening behavior in the post irradiated annealing 304L stainless steel processed by laser powder bed fusion

350 keV He+ ions were injected into laser powder bed fusion (LPBF)–processed 304L stainless steel and traditional rolled 304L stainless steel with a flux of 1×1017 ions/cm2 at room temperature, followed by annealing at 750 ◦C for 10, 100, and 300 h, respectively. The results showed that material swelling due to helium bubble coarsening was almost not observed in either the LPBF or rolled samples after 10 h of annealing duration. Rapid coarsening and swelling of bubbles occurred in the rolled samples, but only moderate bubble growth occurred in the LPBF sample after annealing for 100 h. After annealing for 300 h, the helium bubbles in both samples tended to grow steadily. For 10 h of annealing, the irradiated samples were in a disequilibrium state, and the apparent activation energy (E act) calculated by the Arrhenius model determined that helium atoms tended to diffuse through the displacement mechanism, and helium bubbles grew under the migration and coalescence (MC) mechanism. With annealing times over 100 h, the high-density dislocations and nano-oxide particles in the LPBF sample still had a strong trapping effect on the movement and growth of helium bubbles. After annealing for 300 h, the cellular subgrains in the LPBF sample decomposed, and the nano-oxide particles had no trapping effect on the helium bubbles. At this time, the dislocation structure played a primary role in suppressing the growth of helium bubbles, and the radiation resistance of the LPBF sample remained superior to that of the rolled samples.